The invention relates to a chamber filter press with frameless chamber plates covered respectively on both sides with filter cloths stretched thereover, wherein two adjacent chamber plates contact each other with an outer, continuous clamping rim and define between them a filter chamber, which includes a central filter cake compartment lying between the filter cloths and two outer filtrate compartments lying respectively between the plate and the filter cloth, and with repressing devices for the filter cakes arranged in the zone of at least one of the two filtrate compartments of each filter chamber.
A chamber filter press of the aforementioned type is proposed, for example, DOS No. 2,754,537. The repressing devices set forth therein involve separate press diaphragms stretched over the chamber plates in addition to the filter cloths. In this way, a pressure medium compartment is formed between the press diaphragms and the filter plates; this compartment, due to the high pressing pressures, must be carefully sealed with respect to the outside. A special problem is created in connection with the seal between the pressing medium compartment and the slurry feed ducts and, respectively, filtrate discharge ducts, and for this reason the reference requires special, structurally expensive sealing elements. However, leaks can also readily occur in the remaining zones of the continuous clamping frame since the clamping forces of the pressing diaphragm depend directly on the maximum closing pressure that can be exerted on the plate pack. Due to these difficulties, it is almost impossible to retrofit older chamber filter presses, lacking repressing devices, with press diaphragms.
DOS No. 3,317,235 and DOS No. 3,128,970 disclose frame filter presses wherein press diaphragms are attached between supporting plates and separate clamping frames. As described in greater detail in the aforementioned references, sealing of the press medium compartment is, in this type of structure, simpler than in case of the above-described chamber filter presses, but even in frame filter presses, leakages can develop after a long-term operation due to creep phenomena, and also in these structures, the sealing effect depends decisively on the closing pressure of the press. In any event, however, it is absolutely impossible to retrofit an older frame filter press, lacking repressing devices, by adding frames inserted between the chamber plates inasmuch as thereby the thickness of the plate pack would be unduly increased.
The invention is based on the object of providing a chamber filter press of the type discussed above, the repressing devices of which are simple and economical in manufacture, mounting, and servicing; in this connection, it is also to be possible, in particular, to effect subsequent installation in chamber filter presses at low cost.
This object has been attained according to this invention by providing that the repressing devices are distensible cushions which are suspended within at least one filtrate compartment of each filter chamber at the respectively adjoining chamber plate by way of mounting means keeping open, at least along the lower edge of the distensible cushion, a liquid passage between the half of the filtrate compartment on the filter cloth side and the half on the plate side. By the utilization of distensible cushions, the sealing of the press medium with respect to the slurry feed conduits and the filtrate discharge conduits becomes practically independent of the closing pressure of the chamber filter press. In other words, the closing pressure needs to be only of such a level that, when the distensible cushions are placed under pressure, the plate pack is just barely held together. Additional sealing forces are unnecessary. In the retrofitting of older chamber filter presses, the advantage is thereby obtained, in particular, that the mutually contacting clamping edges of the chamber plates need not be reworked with a view toward sealing of the repressing devices. The suspension of the distensible cushions at the respectively adjoining chamber plate by way of special mounting means takes care of preventing that the distensible cushions, even in the non-pressurized condition, do not collapse and thus retain a perfect positioning with respect to the filter cloths. Due to the liquid connection between the half of the filtrate compartment on the filter cloth side and the half on the plate side, it is finally possible to discharge the filtrate through simple bores on the plate side without the necessity of interposing additional discharge elements between the filter cloth and the distensible cushion.
Although U.S. Pat. No. 270,807 discloses the use of distensible cushions in filter presses, the distensible cushion in the reference is loosely inserted into separate chamber defined on both sides by movable pressure plates which latter are urged against the adjoining filter cloths and thus against the filter cake when the distensible cushion is placed under pressure. The construction set forth in the reference, however, requires an expensive, additional supporting housing for the distensible cushion so that it is unsuitable for retrofitting of older chamber filter presses. Moreover, the pressure plates in the reference can readily be jammed and seized with an even slight change in position of the distensible cushion and/or in case of a contamination of the pressure plate guide means.
DAS No. 1,218,999 also describes a filter press with distensible cushions for pressing out the filter cake. However, in the reference, the distensible cushion is arranged in the filter cake compartment so that two small filter cakes are produced instead of one large filter cake. The small filter cakes, after opening the plate pack, can be detached from the filter cloth only with difficulties due to their low weight. Moreover, in the construction of the reference, an internal supporting ring and an external, additional supporting frame are required for holding the distensible cushion; thereby making retrofitting of older chamber filter presses impossible in any event. Furthermore, the supporting frame impedes washing of the filter cloths when the plate pack is opened up.
According to a preferred embodiment of the invention, the mounting means includes a marginal suspension strip attached at least along the upper edge of the distensible cushion, with the strip being placed around the clamping rim of the respective chamber plate and being suspended via mounting pins or the like at the outer edge of the chamber plate, for example, together with the filter cloths. With the aid of the edge suspension strip, the distensible cushions can be stretched over the chamber plates completely analogously to the filter cloths whereby, during retrofitting of older chamber filter presses, there is no need for additional holding means at the chamber plates. If an exchange of distensible cushions is needed after a relatively long operating period, this servicing work can take place as a matter of routine, just as exchanging filter cloths.
According to the invention, the edge suspension strip can be a permeable fabric strip extending entirely around the distensible cushion. An especially exact positioning is obtained by the all-around clamping mounting of the distensible cushion, remaining the same at all times. Yet, due to the use of a permeable fabric, transfer of filtrate from the half of the filtrate compartment on the filter cloth side to the half on the plate side is ensured.
According to the invention, the edge suspension strip can be provided with several passage openings directly beside the outer rim of the distensible cushion. In this way, transfer of filtrate from the filter cloth to the chamber plate is ensured in any event.
According to an alternative embodiment of the invention, the mounting means may include guide pins projecting from a primary surface of the cushion and being associated with mounting holes provided at the chamber plates. Also in this embodiment, no expensive reworking steps are needed when retrofitting older chamber filter presses, since chamber filter plates are customarily equipped with mounting bores for ducting mats which bores, in this case, can be used for the guide pins of the distensible cushions.
In accordance with a further version of the invention, the filter cloth defining the filtrate compartment accommodating the distensible cushion can simultaneously serve as a mounting means for the distensible cushion, there being provided one or several connecting members between the distensible cushion and the filter cloth. Advantageously, detachability of the connecting members is afforded herein so that the filter cloths, exhibiting a relatively short service life, can be exchanged independently of the distensible cushions.
In another embodiment, the distensible cushion can exhibit a sealed passage opening in the region of a central slurry feed duct on the plate side. In this way, distensible cushions can also be utilized for a widely popular type of construction of chamber filter presses wherein the slurry feed duct extends centrally through the plate pack, i.e. is not extended in the zone of the clamping rim of the chamber plates. When using distensible cushions, no sealing problems are encountered, either, in this structural version, whereas when using simple press diaphragms, sealing is especially problematic precisely in central slurry feed, as demonstrated, for example, by the complicated construction in U.S. Pat. No. 3,888,769.
In accordance with a further embodiment of the invention, the filter cloths, stretched on both sides over a chamber plate, can be joined by way of a filter cloth sleeve in the zone of the central feed duct, and the distensible cushion can include a stiff diaphragm material and can be suspended at the filter cloth sleeve in the region of the cushion passage openings. Since the distensible cushion is supported at all times on both sides in the unpressurized as well as pressurized condition, by the plate and by the pretensioned filter cloth, it is possible by using a stiff diaphragm material to attain a defined positioning of the distensible cushion even without an additional suspension means.
According to the invention, the distensible cushion can exhibit respectively one sealed passage opening in the zone of supporting cogs on the plate side. Adjacent chamber plates thus can come into full contact with each other along their outer clamping rims in spite of the use of distensible cushions whereby satisfactory sealing of the interposed filter chamber remains ensured.
In Accordance with further advantageous features of the present invention, the distensible cushion has, in an area or zone of a slurry feed duct on the plate side and juxtaposed supporting cogs on the plate side, an oval passage opening encompassing or surrounding the supporting cogs and the slurry feed duct.
Moreover, the present invention proposes providing a construction wherein the distensible cushions include two diaphragms in flat contact with each other along their edges which are tightly joined by, for example, welding or gluing.
Advantageously, the distensible cushions are provided on the filter cloth side with ducting in the form of a raised rib system or nubs, grooves, fluting, or the like.
According to the present invention, at least one ducting mat is arranged between the distensible cushion and the filter cloth and, advantageously, the distensible cushions are in communication with a pressure medium conduit which lies outside of the plate pack and is common to all of the cushions by way of a connecting conduit through the clamping rim of the chamber plate.
In accordance with further features of the present invention, the repressing devices may be in the form of distensible cushions which include a stiff diaphragm material and which are arranged within at least one filtrate compartment of each filter chamber, and, at least at the lower edge of the distensible cushion, a liquid passage is provided between the path of the filtrate compartment on the filter cloth side and the half on the side plate.